Offset errors which are subject to change with an operating parameter of an amplifier (e.g., temperature, supply voltage or signal level) may be corrected by use of so-called "chopper" stabilization techniques. In one form of chopper stabilized amplifier the offset is corrected by periodically sampling the amplifier offset with the amplifier input short circuited and using the sampled voltage as a correction signal during a following cycle when the input short circuit is removed.
An example of a chopper stabilized amplifier is described by Redfern in U.S. Pat. No. 4,622,521 which issued Nov. 11, 1986. In the Redfern amplifier a bias voltage is applied to the gate of a common source connected N-channel transistor that is connected in parallel with one load transistor of the amplifier. An offset correction voltage (produced and stored in a capacitor during the amplifier "null" cycle) is applied to the gate of another common source connected N-channel transistor that is coupled in parallel with the other load transistor of the amplifier. In such an arrangement, offset voltage is corrected (nulled) by variation of the load transconductance of one transistor of the amplifier.